Voltage control



March 25, 1941. L. B. HADDAD VOLTAGE cbkTRoL Filed Jan. 22, 1938 INVENTOR Laee J5. Haddad ATTO R N EYS Patented Mar. 25, 1941 UNITED STATES VOLTAGE CONTROL Labeeb B. Haddad, New Haven, Conn.,

assignor,

by mesne assignments, to The Safety Car Heating and Lighting Com pany, Inc., New York,

N. Y., a corporation of Delaware Application .ianuary 22, 1938, Serial No. 186,306 4 Claims. (Cl. 171-119) This invention relates to the treatment of materials and more specifically to an art and apparatus for treating materials by the use of electricity, as well as the control of the electrical 5 power used in such treatment.

One of the objects of this invention is to provide an art and apparatus for carrying on a treatment process which will be thoroughly dependable, practical and efficient in operation. Another object is to provide an art and apparatus of the above character for treating materials in an efficient manner without danger of injury thereto. A further object is to provide apparatus of durable construction which is economical .5 to build and operate. Another object is to provide an automatic control upon the excitation current of an alternator. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, arrangements of parts and in the several steps and relation and order of each of the same to one or more of the others, alias will be illustratively 25 described herein, and the scope of the application of which will be indicated in the following claims. H

In the accompanying drawing, in which is shown one of the various possible embodiments of this invention, the figure is a diagrammatic representation of the electrical circuit and certain of the mechanical parts of an electrical sterilizing apparatus.

Referring to the righthand sideof the figure, illustratively an upper electrode structure 2 is positioned directly over a plurality of electrode rollers 4. Each of the electrode rollers 4 comprises a hollow shell 6 of dielectric material, such as low power-factor glass or quartz, and an elongated electrode element 8 positioned within the dielectric shell. The electrode element 8 comprises the lower electrode structure and c'ooperates with the upper electrode structure 2 to form a treatment zone I 0 therebetween. Apparatus (not shown) is provided for rotating electrode rollers 4, and the packages of the product being treated are placed upon the roller at the extreme right and pass from one roller to another through the treatment zone 10.

A relatively high frequency high potential is impressed across the electrode structures so as to produce a high potential gradient within the treatment zone. This high potential gradient is of such a value that when a package moves into the zone corona-like discharges occur through the package which discharges destroy'all insect life, including the adult, egg, pupa and larva stages. If the potential gradient is too high, spark discharges will occur which may injure the A package or the product being treated. However, 5 this potential gradient must be high enough to thoroughly treat the material and thus it is important that the potential gradient be carefully controlled so that it may be maintained between relatively narrow limits.

The high potential is delivered through an auto-transformer H, the low potential terminal of which is connected through a lead 24 to a ground connection 16, and the high potential terminal of which is connected to the upper electrode 15 structure 2 by a lead I2. Lower electrode elements 8 are connected through individual air condensers 18 to a ground connection 20, thus completing the high potential circuit. Power is delivered to auto-transformer l4 through lead 20 24 and an intermediate potential tap and a lead 26 from. an alternator 22. Alternator 22 is driven through a direct connection by an electric motor 42 which receives its power from a three-phase power source.

There may be variations in the power source which cause changes in the speed of motor 42 and thus of alternator '22. These changes in speed result in changes in the output frequency and voltage and there are corresponding changes 30 in the synchronous reactance of alternator 22 as well as changes in the corresponding capacitative and inductive reactances of the various units within the circuit.

An exciter 46 is directly connected to the shaft of alternator 22 and supplies field excitation current thereto through an adjustable rheostat 48. Thus, if there is a decrease in the speed of alternator 22, there will be a corresponding decrease in its output voltage and at the same time there will be a decrease in the field current due to the decrease in speed of exciter 46. This decrease in field current causes a further decrease in output voltage of alternator 22 and the total change in output voltage may therefore be appreciable even 0 though there is only a small change in alternator speed.

As indicated above, changes in alternator speed result in corresponding changes in the output frequency and apparatus is therefore provided to supply an-additional field current to alternator 22 the value of which depends upon the frequency. Thus, as the voltage tends to decrease due to a decrease in alternator speed, an

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additional field current is supplied to alternator 22 which maintains the voltage constant.

The means for supplying this additional field current is a voltage regulator circuit connected by means of leads ed and as to the output leads 2% and 28, respectively, of alternator 222. This voltage regulator circuit comprises a resistance unit so connected in series with a frequency sen= sitive circuit having two branches. One, branch comprises a resistor 63 in series with a rectifier 53 which is connected by means of leads 8 3 and at, to the terminals 25 and 2a in parallel with exciter so to supply current to the alternator held. The other branch is a frequency sensitive shunt and comprises a resistor l6 and a series inductance unit it connected in series with a parallel resonance circuit. The parallel resonance circuit comprises a condenser Ed and an inductance unit '52, the relative values of which are such that they are in parallel resonance at a frequency somewhat below the normal operating frequency.

At any particular motor speed the alternator field current to give the required generated voltage is determined from the alternator characwristics and the voltage across field terminals 2i andZS is directly proportional to the values of this current and of the field resistance. Furthermore, the exciter voltage generated at this particular speed is known from the enciter char= acteristics, and the percentage of the alternator held current supplied by the exciter depends upon. this voltage and the adjustment oi rheostat 38. Thus, rheostat 38 may be adjusted to give a predetermined voltage drop in series with the generated voltage of exciter 6t and after adjustment this voltage drop varies directly with the field current supplied by the exciter, the value of this current and the exciter voltage varying with changes in speed.

Similarly, the percentage of the alternator field current supplied by rectifier as depends upon the value of the alternating voltage across rectifier 63 and resistor 68 in series, the charac teristlcs of the rectifier and the value of resistor so. This alternating voltage depends upon the frequency which changes with the speed and upon the values of the various units of the regulator circuit, and the values of these units are adjusted to cause the desired direct current to flow through the rectifier to the alternator field at all times.

The output voltage of the alternator is impressed across the voltage regulator circuit and is divided between resistor so and the frequency sensitive circuit in direct proportion to the, rela tive values of the impedances of the two portions of the circuit. In this manner, at the resonant frequency of the parallel resonance circuit, the total impedance of the frequency sensitive circuit is very high and the voltage across this portion of the circuit is likewise very high. As the speed of the alternator increases above this resonant frequency, the impedance of the parallel resonant circuit drops rapidly, but the impedance of re sister 86 remains constant; thus, a large pencentage of the total voltage across the regulator circuit is shifted to resistor es and the voltage across the frequency sensitive circuit drops rapidly. In this manner. the series circuit of rectifier t3 and resistor so is efiectively shunted by the parallel shunt circuit and the voltage thereacross drops.

Resistors 6d and so are adjusted so that the desired value of direct current flows through assures rectifier 68 to the alternator field. By properly adjusting the relative values or condenser ill, inductance malts l2 and lit and resistor E8, the curve along which the impedance of this portion of the circuit changes with changes in frequency is controlled so that the alternating voltage across rectifier and resistor (38, in series, varies along a predetermined line.

in. this manner, at the normal operating frequency a large percentage of the alternator field current is supplied by enciter as and a correspondingly wall portion or this current is supplied icy rectifier (3 As the speed or alternator 22 decreases, the frequency or its output voltage approaches the resonant frequency of the parallel resonant circuit and the alternating voltage across rectifier 353 and resistor lid, in series, is increased causing this circuit to supply an increased current to the alternator field, This resonant frequency corresponds to the alternator speed which is the lowest speed normally reached durling operation and, at this frequency, rectifier 53 supplies a very high percentage of the alternator field current.

As the speed of alternator it rises above the speed corresponding to the normal operating frequency the alternating voltage across rectifier S8 and resistor in series, decreases, and at the frequency corresponding to the maximum speed normally reached during operation, exciter 35 supplies all oi the alternator field current. Thus, it is seen that the voltage regulator circuit is eilective to maintain the field current or alternator 22 at a value to cause its output voltage to remain constant throughout any predetermined range of speeds. In any particular installation, the values of resistors to, lo and 6d and inductance units it and B2 are fixed to meet the particular range of variation in speed and they may also be adjusted to give a rising or falling speed-voltage characteristic.

For example, the normal operation oi this apparatus is air-i920 cycles per second and it has been found that variations may occur in the speed so as to cause the frequency to change between 980 and i060 cycles. The value of inductance unit i2 is adjusted with respect to condenser to so that they are resonant to a frequency of 880 and the values of inductance unit ill and resistances re, so and as are so adjusted that no field current is supplied by the rectifier at 1660 cycles. In this manner the field current to alternator 5.2 is automatically changed inversely as the speed changes and the voltage is maintained substantially constant over a wide range of alternator speed.

' Where the limits of speed variation are differout than those recited, or where a difierent normal frequency is used, it may be desirable to make inductance unit is and condenser 18 resonant to a difierent frequency, either nearer to or farther from the normal operating frequency.

additional apparatus for the control of the potential gradient within the treatment zone may include a condenser for controlling the regulation and correcting for changes in the voltage. lSuch voltage changes may occur due to the synchronous reactance oi alternator 22. With condenser 28, however, the potential gradient is automatically regulated even though there are variations in the load.

A resonance coil 35 is provided in parallel with the input side of auto-transformer is to compensate for the leading current of the autotransformer. This resonance coil draws a lagging current which equals the leading current drawn by auto-transformer H at no load and at a predetermined resonant frequency.

During the starting period, when alternator 22 is being brought up to speed, excessive voltages might be produced due to resonance between condenser 28 and the total equivalent inductive reactance of the circuit; this equivalent reactance includes the synchronous reactance of alternator 22 in series with the equivalent reactance of the parallel circuit formed by resonance coil 38 and auto-transformer H which is highly inductive at low frequencies.

In order to avoid this condition a shunt is provided around condenser 28 which is effective to bypass currents of all frequencies except the frequencies in the range of normal operation.

This shunt comprises a resistor 32 in series with an inductance 36 and a condenser 34. The inductance unit and condenser are in parallel and comprise a parallel resonant circuit which is resonant at or near the normal operating frequency. In this way the shunt carries most of the current until the normal operating frequency is reached and then it is ineffective so that it does not interfere with the normal operation of condenser 28. These various elements including the inductance units 36, 38, 12, H, the resistors 32, 68, I6 and 80 and the rheostat 48, are adjustable and may be made eflective to antomatically control the potential gradient within the treatment zone over a wide range of conditions.

It will thus be seen that I have provided a practical and eflicient system and apparatus for accomplishing the several objects hereinabove mentioned as well as many others in a successful manner.

As many possible embodiments may be made of the mechanical features of, the above invention and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In apparatus of the class described in which a product is treated in a treatment zone by means of electrical discharges resulting from impressing a high electrical potential upon an electrode structure, an alternator which is the source of the electrical potential, an exciter generator to supply alternator field current, and auxiliary means to deliver a variable amount of additional field current to said alternator to thereby control the output voltage of the alternator; said auxiliary means comprising a rectifier circuit having its input side connected across the output side of said alternator and having its output side connected to deliver alternator field current in parallel with said exciter generator,-said rectifier circuit comprising a resistance connected in series with two parallel circuits one of which is a rectifier unit and the other of which is a resonance unit, said resonance unit being in parallel resonance at a frequency slightly below the normal operating frequency of the treating apparatus and the various characteristics of said rectifier circuit having values dependent upon the characteristics of the other apparatus, whereby sufilcient alternator field current is supplied by the auxiliary means at all times to compensate for changes whichoccur due to changes in alternator speed.

2. In apparatus of the class described for supplying current of substantially constant potential to a load, the combination of: an alternator having its main output leads connected to the load; a motive means mechanically connected to rotate said alternator, said motive means having the characteristic that its speed tends to vary with resultant variations in the alternator speed and frequency; an exciter mechanically connected to rotate with said alternator and providing a main source of field excitation current for said alternator; and auxiliary means to prevent variations in alternator voltage which normally accompany changes in alternator speed, said auxiliary means comprising a frequency-sensitive rectifier circuit which supplies field current for said alternator which field current is supplemental to the field current supplied by said exciter, said rectifier circuit comprising a rectifier across the main output leads of said alternator by a frequency-responsive circuit including an inductance means and a capacitance means which are in resonance at a frequency below the normal operating frequency of said alternator, said auxiliary circuit being connected in parallel with said exciter so that as the voltage impressed upon said rectifier is varied as a result of the normal variations in the alternator speed the amount of the alternator field current supplied by said rectifier is varied from substantially zero to a predetermined maximum.

3. In apparatus of the class described for supplying current of substantially constant potential to a load, the combination of:, a generator having its main output leads connected to the load; a motive means mechanically connected to rotate said generatonsaid motive means having the characteristic that its speed tends to vary with resultant variations in the generator speed; primary means providing a main source of field excitation current for said generator; and auxiliary means to prevent variations in generator voltage which normally accompany changes in generator speed, said auxiliary means comprising a frequency-sensitive rectifier circuit which supplies field current for said generator which field current is supplemental to the field current supplied by said primary means, said rectifier circuit comprising a. rectifier unit connected to receive alternating current from said generator through a frequency-responsive circuit, said frequency-responsive circuit including an inductance means and a capacitance means which are in resonance at a frequency below the frequency corresponding to the normal operating speed of said generator, said auxiliary circuit being connected in parallel with said primary means so that as the voltage impressed upon said rectifier is varied as a result of the normal variations in the generator speed the amount of the generator field current supplied by said rectifier is varied from substantially zero to a predetermined maximum.

4. In apparatus of the class described for supplying alternating current of substantially constant potential to a load, the combination of: an alternator having its main output leads connected to the load and having a single field winding circuit, said alternator having the characteristics that its frequency varies with changes in speed and there is a tendency for its voltage to vary with the changes in speed; a motive means mechanically connected to rotate said alternator, said motive means having a source of unit connected power which may vary with resultant verietiane in the speed of said alternator; a primary meme es 2, source of field current fox said altemeaer; and auxiliary means to supply edditienel field eurrent ta said alternator, said auxiliary meezas having its output terminals connectecl in parallel with eaid primary means across said field windins circuit, said auxiliary means comprising rectifier circuit which made up of Wm brencil circuits connected in parallel and in tum cenneczed in series with a resistance unit eemse the main output leads of said alternator, we of said breach circuits including a reefilfier unit and the other oi eeixl branch circuits including" eesm meme unit, said resonance unit being farmed by e eepeciw unit cemented in gemlle; with in (Instance unit and said reeenene-e units being in eizmez'm t0 beeupylieci to 'zhe elitemeioe field winding.

E, HADDAB. 

